Standard Wireline Data Processing
Science operator: Texas A&M University
Hole: U1505C
Expedition: 368
Location: China Sea Rifted Margin (South China Sea)
Latitude: 18°55.0570' N
Longitude: 115° 51.5491' E
Logging date: June 2, 2017
Sea floor depth (driller's): 2928.8 m DRF
Sea floor depth (logger's): 2929.9 m WRF
Total penetration: 3409 m DRF (480.2 m DSF)
Total core recovered: 450.46 m DSF ( 99.7 % of cored section)
Oldest sediment recovered:
Lithology: interbedded foraminifera-rich ooze with clay, nannofossil ooze with clay, and clay-rich nannofossil ooze with foraminifera
The logging data
was recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in June 2017.
| Tool string | Run
|
Top depth (m WMSF) | Bottom depth (m WMSF) | Pipe depth (m WMSF) | Notes |
MSS/HRLA/DSI/HLDS/EDTC-B/HNGS
|
Down |
79 |
Depth reference. Caliper closed. Invald LLDS. |
||
|
Repeat
|
open hole |
||||
Main
|
77
|
The only tool string deployed in Hole U1505C was modified to include the Dipole Sonic Imager (DSI) acoustic tool. This configuration was chosen as it was not expected, based on experience in nearby holes, that the hole conditions would allow a second run including the FMS and acoustic tool. The plan was to log from total depth at 3409 m DRF 480.2 m DSF) but an obstruction was encountered at 3270 m WRF (340.1 m WSF); all attempts to pass the bridge failed, therefore a repeat and main pass were carried out from that depth.
The depths in
the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). Generally, discrepancies may exist between the
sea floor depths determined from the downhole logs and those determined by the
drillers from the pipe length. Typical reasons for depth discrepancies are ship
heave, wireline and pipe stretch, tides, and the difficulty of getting an
accurate sea floor from a 'bottom felt' depth in soft sediment.
Depth shift to sea floor and depth match.
The original logs were first shifted to the sea floor (-
2929.9 m). The sea floor depth
was determined by the step in gamma ray values at 2929.2 m WRF. This differs by 1.1 m from the sea floor depth given by the drillers (see
above). The depth-shifted logs have then been depth-matched to the gamma ray log from thedownlog of the MSS/HRLA/DSI/HLDS/EDTC-B/HNG Stool string.
Depth matching
is typically done in the following way. One log is chosen as reference (base)
log (usually the total gamma ray log from the run with the greatest vertical
extent and no sudden changes in cable speed), and then the features in the
equivalent logs from the other runs are matched to it in turn. This matching is
performed manually. The depth adjustments that were required to bring the match
log in line with the base log are then applied to all the other logs from the
same tool string.
Environmental
corrections. The HNGS
and HRLA data were corrected for hole size during the recording. The HLDS data were corrected hole size respectively during the
recording.
High-resolution
data. Bulk density
(HLDS) data were recorded with a sampling rates of 2.54 cm in addition to the standard sampling rate of 15.24 cm.
The enhanced bulk density curve is the result of Schlumberger enhanced
processing technique performed on the MAXIS system onboard. While in normal
processing short-spacing data is smoothed to match the long-spacing one, in
enhanced processing this is reversed. In a situation where there is good
contact between the HLDS pad and the borehole wall (low-density correction) the
results are improved, because the short spacing has better vertical resolution.
Gamma Ray data from the EDTC-B tool were recorded at sampling rates of 5.08 and 15.24
cm.
Acoustic data. The dipole shear sonic imager (DSI) was operated in the following modes: P&S monopole and upper and lower dipole in all passes. After acquisition, the SLB engineer adjusted the DSI labeling range so that it would pick up the correct peaks consistently. The velocities were computed from the delay times.
The quality of
the data can be assessed by checking against reasonable values for the logged
lithologies, by repeatability between different passes of the same tool, and by
correspondence between logs affected by the same formation property (e.g. the
resistivity log should show similar features to the sonic velocity log).
Gamma ray logs
recorded through bottom hole assembly (BHA) and drill pipe should be used only
qualitatively, because of the attenuation of the incoming signal.
A wide (>12") and/or irregular borehole affects most recordings, particularly those that require eccentralization and a good contact with the borehole wall (APS, HLDS). Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The hole was quite large, with most readings often in excess of 16 inches. The caliper reached its maximum opening in the interval from 96 to 150 m WMSF, therefore the data should be used only from a qualitative stand poimt.
A null value of
-999.25 may replace invalid log values.
Additional information about the drilling and logging operations can be found in the Operations and Downhole Measurements sections of the expedition report, Proceedings of the International Ocean Discovery Program, Expedition 368 . For further questions about the logs, if the hole is still under moratorium please contact the staff scientist of the expedition.
After the moratorium period you may direct your questions to:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia
Tanzhuo Liu
Phone: 845-365-8630
Fax: 845-365-3182
E-mail: Tanzhuo Liu